1. Technical Field of the Invention
The present invention relates to a semiconductor device and, more particularly, to a semiconductor circuit in which semiconductor drivers of different withstand voltage are mixed and disposed within the same chip.
2. Prior Art
A semiconductor switch is used widely instead of a conventional relay and mechanical switch because it is small in size, capable of high speed operation and long in life. As indications representative of the performance of the semiconductor switch, there are withstand voltage, current capacity and on-resistance. By increasing the withstand voltage and current capacity, it is possible to increase treatable power which is a product of them. Further, by reducing the on-resistance, it is possible to decrease heat generation of the semiconductor switch and increase the current capacity under the same heat circumference. Thereby, the energy efficiency can be increased.
The technique for improvement of withstand voltage and current capacity of MOSFET used generally as a semiconductor switch is disclosed in xe2x80x9cApplication Technique of Power MOSFETxe2x80x9d by Hiroshi Yamazaki, issued by Nikkan Industry Newspaper Co. pp. 55-57.
There is an intimate relationship between the withstand voltage and on-resistance of the MOSFET, and according to the above-mentioned literature page 55, there is the following relationship between on-resistance and withstand voltage of unit chip area of a power MOSFET:
Rds (on)/unit chip area  BVds2.4-2.7
where Rds (on) is on-resistance between a drain and a source, and BVds is yield voltage between drain and source. That is, it is noted that when the withstand voltage is increased, the on-resistance increases rapidly in proportion to the 2.4 to 2.7th power of the withstand voltage. Namely, when the element is made so as to have withstand voltage more than the necessity, the on-resistance increases. From this fact, for the power MOSFET, design for optimum withstand voltage meeting with an intended use is important in order to decrease power loss and obtain high efficiency.
Further, in a lateral type power MOSFET, since yield voltage between the drain and the source is proportional to a distance between the drain and source, when the element is made so as to have withstand voltage more than the necessary voltage, a chip area increases. Therefore, the design for optimum withstand voltage meeting with an intended use is important also from a viewpoint of reduction of the chip area.
However, the conventional technique that design and manufacture of a power MOSFET are conducted on the basis of the withstand voltage specification met with an object for its use has the following problems:
(1) Increase of Kinds
The withstand voltage required for a semiconductor element opening and closing a pure resistance load is determined almost by a power supply voltage. According thereto, it is sufficient to prepare a semiconductor element which has withstand voltage corresponding to the power supply voltage. However, the power supply voltage has many different values, so that it is necessary to prepare many kinds of semiconductor elements for only this reason. Therefore, it results to be production of small quantities and many kinds, and a mass production effect can not be brought about.
Further, current is interrupted and flowed for an inductive load such as a motor, a solenoid, etc., whereby counter electromotive force which is Lxc2x7di/dt occurs and the withstand voltage required by the counter electromotive force is determined in many cases. Therefore, it is necessary to prepare semiconductor elements of various kinds according to multiplicity of reactance L and current change ratios di/dt in addition the multiplicity by power supply voltage, thus the mass production effect can not be brought about further.
(2) Bar to Integration
As mentioned above, in the semiconductor element having inductive load, even if power supply voltage is the same, the withstand voltage required for the load differs according to counter electromotive force of Lxc2x7di/dt. For example, on the primary side of an ignition coil of a vehicle engine, although power supply voltage is 12V, the counter electromotive force of the ignition coil reaches several hundreds voltages V, therefore, a semiconductor element having withstand voltage corresponding thereto is necessary for switching.
Further, in the case where drivers formed of a plurality of semiconductor elements are integrated to make the size of a controller small, it is necessary to make each driver have different withstand voltages. In a vertical type MOSFET, a distance between the source and the drain, which influence the withstand voltage, depends on the thickness of a substrate, so that it is structurally impossible to make the same chip have different withstand voltage. Further, in a lateral type MOSFET, a distance from a semiconductor substrate is limited inherently, however, as for a distance between the source and the drain, any distance can be taken in a horizontal direction. However, since diffusion depth and density are necessary to change according to the withstand voltage in order to obtain an optimum characteristic, the number of steps and the number of masks necessary for production increase, whereby a production cost increases, further, a yield rate decreases as the number of steps increases.
The present invention is made in view of the above-mentioned problems, and an object of the present invention is to make it possible to integrate, on the same chip, a plurality of semiconductor drivers having different withstand voltage, thereby to provide semiconductor drivers which can meet various withstand voltage in small kinds, and suppress an increase of the number of kinds of chips due to multiplicity of the withstand voltage.
A semiconductor device according to the present invention which achieves the above-mentioned object, comprises: an embedded insulation layer formed in a semiconductor substrate, a trench isolating between a plurality of power semiconductor elements formed on the semiconductor substrate on the embedded insulation layer and the power semiconductor elements, and an isolator insulating and driving control electrodes of the power semiconductor elements, the above-mentioned semiconductor elements such as transistors can be used, being connected each other in series.